Corrosion behaviour of sintered 6061 aluminium alloy-graphite particle composites.

The corrosion behaviour of sintered 6061 aluminium alloy and its composite dispersed with 7.0 vol% graphite particles is described. Techniques, namely immersion, tafel and impedance, were employed to study the corrosion behaviour. Immersion tests were performed in different media, namely HCl, NaCl and lubricating oil (used and fresh) while tafel and impedance tests were performed in 0.1 N HCl and 3% NaCl solution. Corrosion behaviour was monitored by measuring the weight change in immersion studies and corrosion current, icorr, in tafel and impedance tests. The values of corrosion potential, E corr, and i corr were calculated from the tafel plots obtained at a scanning rate of 1 mV s−1. In impedance study, i corr was calculated from the value of polarization resistance, R p, obtained from the Nyquist plot; the latter was obtained by merging the lock-in and FFT plots. Aluminium alloy and its composite suffered from corrosion in HCl and NaCl. However, the extent of severity was greater in the case of HCl. The i corr values obtained by the impedance method also revealed a similar trend. The higher corrosion rate of the alloy and composites in HCl was due to the dissolution of the thin oxide (protective) film in the solution. The decreased corrosion rate of the composite and the base alloy in NaCl was attributed to the formation of stable corrosion product, Al (OH)3, on the surface, which prevented further attack on the surface of the specimen. There was practically no evidence of corrosion attack on the alloy and the composite surface in used and fresh lubricating oil